Conventionally, disposable diapers (hereinafter referred to as “diapers”) have been produced in a continuous production line. One of processes for producing disposable diapers involves a process in which a plurality of continuous sheets are superposed and an welding process is performed on those sheets in a direction of continuation at a processing pitch of a product unit, thereby joining the plurality of sheets. This process is performed using a so-called sealing apparatus (for example, see JP-A-2006-101970).